In the past, linear motors were of limited applicability to any system needing high speed and power capabilities with large duty cycles because of the many inherent physical design problems of linear motors. Conventional linear motors have had limited applicability to systems controlled and implemented by high speed computers such as robotic measurement and inspection machines.
By their design, conventional linear motors have limited efficiencies because the operative magnetic flux produced can not be fully encapsulated and applied for use as a motive force. Because of their generally rectangular design and open drive path, linear motors lose much of the magnetic flux produced by their coils and primary cores to the surrounding environment, unlike typical rotary motors which are able to concentrate the magnetic flux produced within a closed rotary drive path.
In order to perform measurement or inspection tasks at a cost effective high rate of speed and at a significant power, large amounts of current are required to drive the linear motors which, because of their inherently inefficient design, resulted in large heat buildups causing not only motor failure but physical deformation of the surrounding machine. In order for a linear motor to be used at a high speed for a long period of time, the current must be increased. However, as the current increases two-fold the heat produced by the motor will result in an increase by the square, or four-fold in this example, resulting in linear motors being unacceptable for many applications. For example, if a conventional linear motor is operated at a high speed for a long period of time, the motor's temperature would greatly increase causing the geometrical dimensions and tolerances of a measurement and inspection machine to deform, providing inaccurate and unreliable data.
Conventional linear motors for use in highly accurate measurement and inspection systems have been operated inefficiently at low currents and therefore slow speeds so that the motor temperature would remain relatively constant at a low temperature. In order to perform high speed measurements and inspections, such as in a manufacturing environment where 100% inspection is required, the linear motor must be operated at high currents with high duty cycles resulting in high motor temperatures with substantial risk that the motor will fail or the machine will deform and be out of tolerance providing inaccurate temperature data. Therefore, in many critical temperature applications, linear motors have had very limited applicability because of the resulting heat generated from their use at high speeds for long time periods.
Additionally, the problem of cooling motors of this type have been addressed in the past by attempting to cool the exterior of the motor. These methods have afforded some minor improvement, but were unable to remove enough heat to run a linear motor at high speed with sufficient power and a sufficiently large duty cycle under the control and implementation of a high speed control system or computer.
Other driving methods for high speed inspection and measurement systems have used belt, rotary leadscrew, friction or rack and pinion drives. These types of drives do not afford the accuracy, reliability and duty-cycle needed for many critical high speed and high accuracy systems, especially in computerized state of the art robotic inspection and coordinate measurement systems.